Integrin antagonists induce caspase-3– and -8–dependent apoptosis in vivo. (a–d) CAMs stimulated with saline or bFGF were treated with 2.5% DMSO (vehicle control), anti-α5β1, or anti-α5β1 with 500 μM caspase-3 (a and b) or caspase-8 (c and d) inhibitors. (a and c) Blood vessel branch points were quantified after 48 hours. (b and d) Caspase-3 and -8 cleavage was evaluated by Western blotting with (b) anti–cleaved caspase-3 or (d) anti–cleaved caspase-8 Ab’s and anti-actin Ab’s. (e) Cryosections of CAMs treated as in a–d were immunostained for vWF expression (red) and to detect DNA fragmentation (TUNEL staining, green). Arrows indicate blood vessels. Apoptotic vessels appear yellow.